<div class="panel panel-primary">
  <div class="panel-heading">这是子组件</div>
  <div class="panel-body">
    <button (click)="dec()" title="smaller">-</button>
    <button (click)="inc()" title="larger">+</button>
    <span [style.font-size.px] = "size">FontSize:{{size}}</span>
  </div>
</div>